Electrolytic condenser



sept- 1942. P. ROBINSON T 2,297,669

ELECTROLYTIC CONDENSER Filed Jan. 27, 1940 PRESTON ROBINSON AND JOHNBURNHAM BY m (3 4, 5L ga/r M/ ATTORNEY 5 Patented Sept. 29, 1942ELECTROLYTIC CONDENSER Preston Robinson, Williamstown, and John Burnham,North Adams, Mass.

Application January 27, 1940, Serial No. 316,033

7 Claims.

The present invention relates to electrolytic condensers suitable foroperation in alternating current circuits. More particularly ourinvention relates to a new and novel electrolytic condenser of theso-called A. C. dry type suitable for continuous operation in A. C.circuits.

Prior condensers of this type usually comprise as their main elementstwo electrodes of a filming metal on which is electrolytically formed adielectric film. As is well known, the two filmed electrodes of an A. C.electrolytic condenser are always charged positive with respect to theelectrolyte and because of this such electrodes are referred to asanodes. Disposed between the anodes is a spacer of an absorbent materialwhich also serves as a carrier-for the electrolyte. The anodes, togetherwith their interposed spacers are usually wound to form a condenserroll, although they may be assembled as a stack. The electrolyte usedmay have a viscosity ranging from that of a viscous fluid to that of asemisolidpaste.

Heretofore dry electrolytic condensers have been restricted in their useto circuits involving their intermittent operation only. For example,condensers of this type have been used to a considerable extent asstarting condensers of capacitor motors, where in such application, theyare subjected to short intermittent use and to comparatively lowvoltages.

Attempts to use dry electrolytic condensers for continuous operationand/or at higher voltages, have not been successful, as the priorcondensers fall after short periods of operation, and the higher thevoltages the shorter these periods. The main reason for this is theheating up of the condenser, due primarily to its comparatively high andunstable power factor; such heating up causing a progressive and rapiddeterioration of the condenser. While artificial means to increase theheat dissipation of the condenser have been suggested, for example, bymeans of oil cooling, as described in U. S. Patent #1,992 .545 toPreston Robinson, such means are comparatively expensive and not alwayspractical.

Another solution of this problem, namely the use of a series combinationof a plurality of such condensers, has been described in U. S. Patent#2,0l1,l26 to Robert C. Sprague. However, series operation ofelectrolytic condensers introduces the outstanding difficulties of areduction in capacity to a value inversely proportional to the number ofcondensers connected in series, and an increase in the number ofcondenser units requlred.

The present invention which will be described in connection with a woundcondenser, obviates the difficulties of prior condensers, and permitsthe operation of A. C. electrolytic condensers in continuous service andat high voltages and this without requiring a plurality of condensersbeing operated in series arrangement.

The novel A. C. electrolytic condenser of our invention is characterizedby a very low and stable power factor and low electrical losses, wherebysuch losses as exist are easily dissipated by the condenser and theheating up and consequent destruction thereof is prevented.

As a result of a comprehensive investigation of prior A. C. electrolyticcondensers, in an effort to determine the causes bringing about the veryhigh and unstable power factors and losses thereof we have found thefollowing:

The general assumption that the current flows from one anode to theother in a straight line path through the electrolyte, and that theseries resistance and hence the power factor of the condenser isdetermined by the length of this straight line path, is erroneous. Wehave found on the contrary, that in the proximity of and at the edges ofthe anodes there exists a fringe eifect, causing the current path in theelectrolyte at these edge zones to be many times longer than thedistance between the anodes.

This fringe effect we have found, is greater the greater the distancebetween the anodes, and iurthermore all other factors being equal, thepower factor of the condenser increases with the fringe effect. 1

The fringe effect manifests itself both at the side edge zones and theend edge zones of the anodes. This is due to the fact that at the endedge zones of the anodes there is no immediately adjacent portion of theother anode. At the side edges of the anodes a similar condition existsbecause of the dielectric film formed on the surface of the edgeportions.

While as a rule because of the length of the anode strips, the area ofthe side edge zones is greater than that of the end edge zones, we havefound that the influence of the fringe eifect caused by the latter aloneis unexpectedly high.

As a result of our investigations we have found that a substantialreduction of the power factor of an A. C. dry electrolytic condenser canbe achieved by eliminating the fringe effect and causing all of thecurrent to flow through the electrolyte in a path substantiallyperpendicular to the surface of the anodes.

In accordance with our invention we achieve the above results byinterposing between the anodes floating electrodes having surfacedimensions greater than those of the anodes and extending well beyondthe corresponding edges of the anodes and preferably even beyond theelectrolyte, respectively the electrolyte carrying spacer. Thus theedges of the floating electrodes extend not only beyond the side edgesof the anodes but also beyond the end edges thereof whereby they overlapat least one anode turn at the inner and outer ends of the condenserroll. This provides that every portion of each anode is opposed by acorresponding portion of a floating electrode.

To get the full benefits of our invention, the floating electrodesshould be of a non-filming character, for example, made of a non-filmingmetal such as chromium, nickel, silver, tin or lead, and which do notform soluble salts in the particular condenser electrolyte used.

Instead of using the metals themselves they may be applied as a platingor coating on other metals, for example, on aluminum or iron.

Our invention will be further described with reference to the appendeddrawing in which:

Figure 1 is a perspective view of an A. C. condenser in accordance withthe invention.

Fig. 2 is a cross-sectional enlarged view of an element taken along theline 2--2 of Fig. 1.

Referring to the drawing, the condenser shown therein comprises twoanodes I and 2 each of a filming metal and preferably of aluminum foil.Interposed between adjacent faces of the anodes I and 2 are two spacers3-3 and between these spacers is a floating electrode 4. Similarlybetween the opposite faces of the anodes I and 2 there are two spacers6-6 and between these spacers is a floating electrode 1. For theiroutside electrical connection the anodes I and 2 are provided withterminal tabs 8 and 9 respectively.

The anodes I and 2 may have their surfaces etched by known processesafter which, whether etched or unetched, they are provided with adielectric film by means of a suitable forming process in a suitableforming electrolyte, for example, as described in U. S. Patent#2,116,449 to Preston Robinson.

The forming voltage used depends on the voltage at which the condenseris to be operated. For example, with condensers to be operated at avoltage of 110 volts A. C., we form the anodes to a voltage of 160volts.

The absorbent spacers may be of gauze, paper, Cellophane and the likeand serve as carriers for a viscous electrolyte of the condenser.

The electrolyte 5 is as a rule viscous whereby the viscosity may varyfrom that of a semiviscous fluid to that of a substantially hard mass.As a rule. we prefer to use an electrolyte having at room temperaturethe consistency of a paste.

The impregnation of the condenser with such electrolytes takes place inwell-known manner and preferably after its assembly.

The floating electrodes as previously stated, are preferably of anon-filming metal such as chromium, nickel, tin or the like, or of afilming metal such as aluminum or of a non-filming metal such as iron orcopper, provided with a plating or coating of one of the first mentionedmetals.

In accordance with the invention the floating electrodes have dimensionsgreater than those of the anodes I and 2 and extend well beyond both theside and end edges ofthe anodes and preferably overlap at least one turnthereby encircling and enclosing the anodes as shown in Fig. 1.

Fig. 2 shows the electrodes 4 and 1 extending beyond the side edges ofthe anodes I and 2 and even beyond the electrode impregnated spacers 3-3and 6-6.

Instead of rolled condensers other assemblies such as stacks may be usedin which case to obtain the full benefit of the invention it isessential that the stack be terminated at each end by a floatingelectrode and that preferably all the floating electrodes beelectrically interconnected.

The outstanding advantages achieved by the invention may be more fullyrealized when it is considered that a condenser of the prior artcomprising etched anodes formed to 160 volts and having a capacity valueof 40 microfarads, has an average life of approximately 10 hours whenoperated in continuous service at volts A. C. A similar condenser madein accordance with the invention operates under the same conditions inexcess of 2500 hours.

While we have described our invention in a specific embodiment and bymeans of a specific example, we do not wish to be limited thereto forobvious modifications will occur to those skilled in the art withoutdeparting from the spirit and scope of the invention.

What we claim is:

1. An A. C. electrolytic condenser comprising two filmed anode foils, aviscous film-maintaining electrolyte and floating electrodes embedded insaid electrolyte and interposed in spacial relationship between andcoextensive with said anodes, said electrodes having surface dimensionsgreater than those of said anodes and extending beyond all edges of saidanodes.

2. An A. C. electrolytic condenser comprising two filmed anode foils, aviscous film-maintaining electrolyte, and non-filming floatingelectrodes embedded in said electrolyte and interposed in spacialrelationship between and coextensive with said anodes, said electrodesbeing immune against attack of the electrolyte in operation and inidleness of the condenser and having surface dimensions greater thanthose of said anodes and extending beyond all edges thereof.

3. An A. C. electrolytic condenser comprising two convolute filmed anodefoils, a viscous filmmaintaining electrolyte, and floating electrodes ofa non-film-forrning metal embedded in said electrolyte and interposed inspacial relationship between and coextensive with said anodes, saidelectrodes being immune against attack of the electrolyte in operationand in idleness of the condenser and having surface dimensions greaterthan those of said anodes whereby said electrodes extend beyond alledges of said anodes.

4. An A. C. electrolytic condenser comprising two convolute filmedanodes, a viscous filmmaintaining electrolyte and means to decrease thepower factor of said condenser said means comprising floating electrodesembedded in said electrolyte and interposed in spacial relationshipbetween and coextensive with said anodes, said electrodes having surfacedimensions greater than those of said anodes whereby said electrodesextend beyond all edges of said anodes.

5. An A. C. electrolytic condenser comprising two convolute filmedanodes, a viscous film-maintaining electrolyte and means to provide astraight line current path through said electrolyte, said meanscomprising floating electrodes interposed between and coextensive withsaid anodes in said electrolyte, said floating electrodes having surfacedimensions greater than the dimensions of said anodes and extendingbeyond all edges of the anodes.

6. An A. C. electrolytic condenser comprising two convolute filmed anodeelectrodes, and a viscous film maintaining electrolyte disposed betweensaid anodes, floating electrodes interposed between said anodes andembedded in said electrolyte each of said floating electrodes havingsurface dimensions greater than the surface dimensions of each of saidanodes, extending beyond all edges of the anodes and symmetricallyinterwound with said anodes, said electrodes having a length in excessof said anodes and each portion of an anode surface having opposite toit an adjacently disposed portion of a floating electrode.

7. An A. C. electrolytic condenser comprising two filmed anode foils, afilm-maintaining electrolyte and floating electrodes interposed betweenand coextending with said anodes, said electrodes having surfacedimensions greater than those of said anodes and extending beyond alledges of said anodes.

PRESTON ROBINSON. JOHN BURNHAM.

